The graphic arts industry, including the printing industry, has increasingly automated its means for generating plates for printing of pictures in line, black-and-white halftone and in color. In common use today are devices known as "scanners," in which an original image or "copy" is placed on a rotating drum and scanned for reflected light intensity within defined areas (screen analogs) serving as pictorial elements or "pixels." (By using different colors of incident light, or by filtering, color separation may be achieved for color printing). The information is generally reproduced on a plate or film, often on the same rotating drum, by a writing mechanism such as a laser. As an intermediate step, the information may be further processed, for example, rotated to simulate traditional mechanical screen separation. In the scanners commercially available today, certain portions of this information processing are incorporated within the scanner/writer device.
Because it is desirable to perform additional processing of the pictorial information, such as that allowing picture enhancements, corrections and page layout and make-up, it is common to load the data output of the scanner device into a separate mini- or microcomputer (and related storage devices) to allow processing and previewing of the image to be written.
The data output of a typical scanner are digital, multi-bit, representations of intensities of scanned colors, typically, Red, Green, and Blue ("R", "G", and "B"), for each pixel, plus additional data for image enhancement known as an "Unsharp Mask" or "USM." Each multi-bit representation of a color intensity for a pixel may be called a "pixel value."
Input to the writer portion of a scanner/writer typically include pixel values for each of the Yellow, Black, Cyan and Magenta separations. The separations may be generated "simultaneously" on contiguous regions of the drum, e.g., in "two up" or "four up" configurations, with each scan writing a line (sometimes called a "subline") of each of the multiple separations.
Transmission of data to and from the input/output device is usually accompanied by a "handshake." In the case of synchronous transmission, this may be a "request" signal accompanying data transmission, with the negating of the request signifying the end of a particular transmission. In asynchronous transmission, the handshake may be a request from the transmitting device and an "acknowledgement" from the receiving device.
Because many pixels are required to provide acceptable resolution, and there may be multiple pixel values for each pixel, it can be seen that a high rate of data transfer is required in order to scan and write within a reasonably limited period of time. This data rate is generally greater than that which can be handled by most processors. Therefore, intermediate storage means, or "buffers," may be employed in both the scanning and writing phases of pictorial information processing.
Different input and output devices may use different data formats and buses (8 or 16 bits) and different data transfer handshake protocols (synchronous or asynchronous). Examples of input and output devices other than scanner/writers include line art digitizers and plotters.
Previously, the interface between the graphic input/output device and the information processor was "dedicated" to the input/output device, allowing for high speed data transfer. A change in the input/output device would require a different interface and perhaps rewiring within the input/output device. If, for example, only blue values were to be captured, such editing would have to occur at the processor level, wasting the transmission bandwidth in transmission of the Red, Green and USM information.
It is a purpose of the present invention to provide a flexible, but efficient, interface between a graphic input/output device and an information processing and previewing system. The present invention allows interface with input/output devices with different data formats and handshake protocols with no rewiring. The invention further allows rearrangement of the pictorial data in a format that maximizes the rate of transmission, for example, by eliminating the USM information, which often is not used at the processor level.